Venue: Physics and Astronomy Seminar Room
Abstract:
The closest composite Seyfert–starburst galaxies, NGC 1068, the Circinus galaxy, and NGC 4945, were observed by the High Energy Stereoscopic System (H.E.S.S.) to look for very-high energy (VHE; > 100 GeV) γ-ray emission. Composite galaxies, containing both a starburst and Seyfert component, may produce VHE gamma rays at vastly different spatial scales ranging from several Schwarzschild radii of a supermassive black hole (SMBH) to a dozen kiloparsecs. For a variety of scenarios VHE γ-ray observations are expected to provide stringent constraints on cosmic-ray populations in these systems. No signals were found in the H.E.S.S. data. We derive upper limits on the VHE γ-ray fluxes compare them to a variety of possible emission models. The H.E.S.S. observations of the nearby composite Seyfert-starburst galaxies probe a broad range of energetic astrophysical phenomena. The non-detection of NGC 1068, the Circinus galaxy, and NGC 4945 in the H.E.S.S. data has implications on the cosmic-ray populations existing under different physical conditions.
Brief Biography:
Andrew Chen was born in New York City, USA in 1970. After receiving his PhD from Columbia University in 1997 and a postdoctoral fellowship at NASA Goddard Space Flight Center, he moved to Milan, Italy to work on AGILE, the Italian Space Agency gamma-ray space telescope. He moved to South Africa in 2013 to become part of the Astrophysics group in the School of Physics at Wits. Prof Chen's field of research is observational multiwavelength, multimessenger and high-energy astrophysics, with an emphasis on extragalactic astronomy, including AGN and radio galaxies. He is a member of international collaborations such as AGILE, Fermi, H.E.S.S., KM3NeT, and CTAO.
Contact Professor Roberto De Propris (deproprisr@biust.ac.bw) for enquiries.